During regular operation in a memory module, there are a plurality of subcircuit blocks which are actually not utilized. These subcircuit blocks are usually arranged in a specific region of the memory module and characterized by a functional effect.
Thus, the fact of which functional subcircuit blocks are active at a given point in time in a memory module is generally dependent on external commands. For example, the circuits for tests of the memory cell array are only active in a test mode, and not during regular operation.
Moreover, in a memory module of a modern generation, the individual subcircuit blocks usually wait for a new command. Thus, in the “precharge power down” phase of a semiconductor memory module, in which the semiconductor memory waits for a read or write command, the functional subcircuit blocks for the row or column decoding and also the functional block for the data path are deactivated.
Despite their logical deactivation, the inactive subcircuit blocks of a semiconductor memory consume a small current, which is called a leakage current and is usually of the order of magnitude of a few μA. In a standby operation, in which only few circuit parts are actively operated, the leakage current proportion rises rapidly in comparison with the switching current proportion.
The cause of such leakage currents has both technological reasons, for example, contaminants in the semiconductor material, and physical reasons, for example, thermal generation of the charge carriers. At feature sizes of <100 nm, the leakage current is expected to rise rapidly on account of these effects. At these small feature sizes, quantum mechanical effects such as tunneling currents, for example, additionally arise and increase the leakage current further.